Proanthocyanidin is a substance which is contained in many plants and is known to have strong antioxidant action. However, it is known that this substance is unstable in the presence of oxygen. That is, oxidative polymerization etc. rapidly occurs in the presence of oxygen, which discolors the proanthocyanidin.
A known method for stabilizing proanthocyanidin in a wine includes admixing a wine with potassium pyrosulfite. A known method for stabilizing proanthocyanidin in an apple juice includes admixing an apple juice with ascorbic acid. Also, JP-A-6-336420 (the term “JP-A” as used herein means an unexamined published Japanese patent application and “JP-B” means an examined published Japanese patent publication) discloses a cosmetic in which sodium hydrogen sulfite, 1-hydroxyethane-1,1-disulfonic acid, and diethylenetriaminepentaacetic acid or phytic acid are employed in order to prevent coloring of proanthocyanidin with passage of time.
In addition, as methods or compositions for stabilizing polyphenol or for preventing their discoloration, (1) JP-B-8-2819 discloses a method for preventing discoloration of polyphenol by mixing a porphyrin-zinc complex and an organic reducing agent, (2) JP-A-5-112441 discloses a cosmetic for the skin in which a polyphenol compound is mixed with a sucrose-higher fatty acid ester, (3) JP-A-5-163131 discloses a cosmetic for the skin in which a polyphenol compound is mixed with an alkyl glucoside and (4) Japanese Patent No. 2,744,572 discloses a method for preventing discoloration of an external skin preparation containing a polyhydric alcohol or saccharides mixed with a polyphenol compound having three or more phenolic hydroxyl groups.
The object of the invention is to provide a method for stabilizing proanthocyanidin, particularly for preventing, for example, its discoloration by oxidative polymerization. The object of the present invention is also to provide a proanthocyanidin-containing composition having excellent stability, as well as a drink, a food, a cosmetic or a medicament which contains the composition.